To me the main advantages for me to bill monthly is:
1. I can plan and budget effectively. All of the monthly clients sign a legal, binding agreement - some for 2 years.
2. It keeps the customers monthly bill smaller.
3. It gives me revenue in the off season (Dec - Mar for me)
4. It takes the guess work out of the schedule. It's not up to the client to try and save a buck and skip a week. We have some every 2 week cuts; but they pay a premium. Many times it takes as long to mow a yard once every two weeks as mowing twice - the grass clippings have to be bagged, etc.